1. Field of Invention
The field of this invention relates to devices that produce useful work from hydraulic pressure, and more specifically devices that do useful work while hydraulic pressure is removed.
2. Description of Prior Art
The disclosed flexible hydraulic muscle is designed to extend while being pressurized with a hydraulic fluid and contract strongly when pressure is released. This is the exact reverse of known prior art, where flexible hydraulic muscles are designed to retract when hydraulic pressure is applied, and extend when pressure is released. To provide the reverse, systems can use negative pressure to contract the muscle, however these are limited to one atmosphere of force (14.7 per square inch). Bellow systems for use with actuating levers sometimes use this negative vacuum pressure to provide a retracting force, but such force is limited and requires a large system to provide large forces. Bellows may also work with pressurized air to providing a retracting force, but requires a cylinder housing and piston which does not allow the bellow to be flexible or light-weight. No known flexible bellow system was found that provides its strongest contracting force while hydraulic fluid pressure is released. Also, no known hydraulic muscle was found which uses a liquid hydraulic fluid to provide a contracting force during pressure release. The Applicant has another patent application Ser. No. 10/303,941 (US 2003/0098084 A1) titled “Pressure-Actuated Linearly Retractable and Extendible Hose” which is for a similar device. Application Ser. No. 10/303,941 is specifically for hoses for transporting a fluid (gas or liquid) from one end to the other, and generally never flows in the opposite direction. For the Disclosed hydraulic muscle it is actually a disadvantage to transport fluid from one side to the other since this would require an additional fluid return line that is not needed. One could connect two muscles adjacent to each other and in parallel so one functions as a return line, but the fluid would still be recirculating and not actually being transported for external use.
The use of liquid hydraulic fluid, such as oil-base fluids, allow much higher operating pressures than are possible with gas-based systems. However, the flexible nature of the hydraulic muscle (without support guides) prevents it from generating significant extending force. Though strong extending force can be generate if lateral stiffening guide(s) (lateral stiffening supports) are used to prevent the muscle from bowing out of alignment. Without side support guides the muscle can simply bend in the middle. Once extended, strong tension biasing exists within the muscle, but is held in place by hydraulic pressure. When hydraulic fluid is released, this tension biasing causes a strong contracting force within the muscle. For purposes of this patent, the term hydraulic fluid will be used to refer to both liquid and gas working fluids (hydraulic and pneumatic systems).